Erasable media is that which can be reused many times to transiently store images, the images being written on and erased from the erasable media. To make erasable media as useful as possible, it is important to enable erasable annotation. Although the user can write on the erasable media using a conventional pen or pencil, these marks of course will be permanent and reduce the usefulness of that erasable medium for future reuses. A number of approaches have already been used to circumvent this using either an external LED pen or an internal LED pen. A first approach is a UV LED built into a pen that can be used to write directly on the paper. A second approach is using an ink placed in the barrel of a pen (e.g. a fountain pen) and colorizing the ink on writing by a UV LED locked inside the pen barrel. Once on the erasable medium, the handwriting fades and colorizes at a similar rate as the erasable media. Although both methods are suitable for annotation, each requires a power supply built into the pen in order to activate the LED. The LED requirement makes the ink incompatible with conventional fountain pens, ballpoint pens, and other writing implements. Hence there is a need for a photochromic ink which does not require activation using a UV LED. This will not only eliminate the need for a battery, but will reduce costs.
Thus, there is a need to overcome these and other problems of the prior art and to provide erasable ink compositions and methods of making erasable annotations.